feat(builtins): implement JsGeneratorFunction safe wrapper

[KaustubhOG]

Implements the JsGeneratorFunction safe Rust wrapper as part of #2098.

Adds core/engine/src/object/builtins/jsgeneratorfunction.rs with:

• from_object(object: JsObject) -> JsResult<Self>
• call(this, args, context) -> JsResult<JsValue>
• From<JsGeneratorFunction> for JsObject and JsValue
• Deref to JsObject
• TryFromJs impl

GeneratorFunction has no JsData derive, so type detection uses
downcast_ref::<OrdinaryFunction>() and checks code.is_generator() && !code.is_async().

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,862	52,862	0
Passed	49,505	49,505	0
Ignored	2,261	2,261	0
Failed	1,096	1,096	0
Panics	0	0	0
Conformance	93.65%	93.65%	0.00%

[codecov]

Codecov Report

❌ Patch coverage is 0% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.01%. Comparing base (6ddc2b4) to head (f7b0604).
⚠️ Report is 705 commits behind head on main.

Files with missing lines	Patch %	Lines
.../engine/src/object/builtins/jsgeneratorfunction.rs	0.00%	25 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4756      +/-   ##
==========================================
+ Coverage   47.24%   57.01%   +9.77%     
==========================================
  Files         476      553      +77     
  Lines       46892    60593   +13701     
==========================================
+ Hits        22154    34547   +12393     
- Misses      24738    26046    +1308     

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[jedel1043]

Very nice! Thank you!

[KaustubhOG]

Hi @jedel1043, thank you for the quick review and guidance throughout these PRs — your feedback has been very clear and helpful. Really appreciate your support! thanks again ( whenever u get chance take a look at #4755 the only wrapper that is remaining in our original #2098 )